The south Pacific iguanas (Brachylophus) currently have three recognized living species in Fiji. Recent surveys have uncovered more specific variation (morphological and genetic) within the genus and have better defined the geographic ranges of the named species. One of these recent discoveries is a strikingly different iguana from all other island populations in Fiji which is restricted to Gau Island of the Lomaiviti Province. Gau is the fifth largest island in Fiji and maintains excellent upland forests in the higher elevations. We describe this population from Gau Island as a new species, Brachylophus gau sp. nov., in recognition of its type locality.

FIGURE 2. Illustration of the holotype (SUVA H 0264; left) and paratype female (SUVA H 0265; right) of Brachylophus gau sp. nov. The painting is from photographs of these specimens and others from life. Measurements to scale within illustration. The holotype is missing later 2/3 of tail, but tail drawn here based on photos from other males.

Diagnosis. This species has a unique combination of color pattern characters that distinguish it from all other species of described Brachylophus (Figures 2–7, Table 1). It also does not match any museum specimens we have previously seen in collections, except two from the BMNH that previously lacked specific locality info. These specimens are included in the type series as we were able to determine their provenance as Gau Island (see below in Provenance of Historic Specimens section). Although added to the type series, their measurements are left out of comparisons, but included in Table 2. We found that there are no locality specific museum vouchers that could represent extinct island populations of this species. Otherwise, this species differs from B. vitiensis by having sexually dichromatism, with banded males and females that are either unicolor or with small spots, and a maximum snout vent length for both sexes of 153 mm, versus 255 mm for B. vitiensis. It differs from B. bulabula and fasciatus in that males and females have green throats, whereas in these species males have white solid or white with green/grey spots or blotches, as do the females in most populations. Although in certain populations the females in B. bulabula and fasciatus the throat will be unicolor green, but never the males. It differs from the other three species by having a primarily green colored nasal scale. The mean snout vent length is 149.2 and max size for B. gau is 153 mm (n = 7), versus adult B. fasciatus with a mean 154.5 mm SVL and a maximum 176 mm SVL (n = 57) and B. bulabula with a mean 156.6 mm and a maximum 195 mm SVL (n = 23) (Table 1).

Etymology. The specific epithet is for the only island where the species is known to occur, Gau.

Distribution. Brachylophus gau appears restricted to the large inland forest patches on Gau Island (Figure 1).
Iguanas were reported from Gau by Watling (1986), but no specimens were collected or described. It continues to
be widespread in high quality forest habitat in the interior of Gau Island (Figure 8), with some individuals also in
degraded forest closer to the coast (Figure 9). Gau is about 136 sq. km. in size and is the fifth largest island in Fiji.